Apparatus and method for an analog-to-digital converter having a programmable trigger level

ABSTRACT

In response to a selected analog applied to the input terminal of an analog-to-digital converter, the digitized output signal is stored in a buffer/register. In making a comparison with a predetermined value, a second buffer/register stores either a preselected value or a second digitized signal. A comparator is coupled to the first and the second buffer/register to provide the result of a comparison. In this manner, the central processing unit is not involved in the comparison testing procedure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to analog-to-digital converts and, more particularly, to using an analog-to-digital converter in a programmable trigger level comparison configuration.

2. Background of the Invention

In many important applications, the level of a signal should be constrained by predetermined values. For example, when the oil pressure in a motor rises above a certain level, a response is called for. That response can be a warning signal to the user or can be a more direct response involving the motor itself.

Referring to FIG. 1, the use of an analog-to-digital converter 15 to provide an activity upon a predetermined comparison with a voltage level is shown. A series of signals are applied to input terminals 11A-11N of a multiplexer 12. A sequence/control unit 14 selects the input terminal 11A-11N to be applied to an analog-to-digital converter 15. The output signal of the analog-to-digital converter 15 is applied to switch 16 under the control of the sequence/control unit 14. The configuration of the switch 16 determines into which of the buffer/registers 17A-17M the output signal of the analog-to-digital converter 15 is stored. In response to a signal from the sequence/control unit 14, an interrupt is provided to the central processing unit 18. In response to this interrupt signal, the central processing unit 18 retrieves the contents of a preselected one of the buffer/registers 17A-17M and compares the stored value in the buffer/register with a predetermined value stored in the central processing unit 18. When the comparison is positive, the central processing unit 18 generates an interrupt signal to respond to the identified condition and then continues the execution of the programmed procedures.

The foregoing procedure has several features that affect the efficiency of the program execution of the central processing unit 18. In particular, the necessity for interrupting the executing program of the central processing to determine whether an interrupt signal should be generated is typically wasted time when the condition to generate and interrupt signal are not present.

A need has therefore been felt for apparatus and an associated method having the feature of a comparison of a digitized signal with a predetermined value. It would be yet another feature of the apparatus and associated method for comparing a digitized signal with a predetermined value without the intervention of the central processing unit. It is yet another feature of the apparatus and associated method to generate an interrupt signal without disrupting the operation of the central processing unit.

SUMMARY OF THE INVENTION

The foregoing and other features are accomplished, according the present invention, by providing a selectable input signal for an analog-to-digital converter. The digitized output signal of the analog-to-digital converter is stored in one of a second plurality of buffer/registers. Associated with each of the second plurality of buffer/registers is an associated buffer/register. The associated buffer/register stores a value against which the contents of the buffer/register is to be compared. According to a first embodiment of the invention an associated buffer/register stores a preslected value. According to a second embodiment, the associated buffer/register stores a digitized signal that has been applied to the analog-to-digital converter, the input signal having been selected by a sequence control unit. The contents of the buffer/register and the associated buffer register are applied to a comparator unit. The result of the comparison, when the comparison provides an expected result, is to generate an interrupt signal, the interrupt signal being applied to the central processing unit in order to respond to the expected condition.

Other features and advantages of the present invention will be more clearly understood upon reading of the following description and the accompanying drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the apparatus for determining the results of a comparison between a digitized signal and a preselected signal according to the prior art.

FIG. 2 illustrates the apparatus for comparing a digitized signal with a preselected digital value without requiring a central processing unit according to the present invention.

FIG. 3 illustrates apparatus for comparing two digitized signals according to the present invention.

1. DETAILED DESCRIPTION OF THE FIGURES

FIG. 1 has been discussed with respect to the related art.

Referring next to FIG. 2, a block diagram of the first embodiment of the present invention is shown. Signals are applied to input terminals 11A-11N that are coupled to the input terminals of multiplexer 12. Control signals from sequence/control unit 24 determine the input signal applied to analog-to-digital converter 15. The output terminal of the analog-to-digital converter 15 is applied the digitized output signal to switch 26. In response to control signals from sequence/control unit 24, the switch directs the digitized signal from the analog-to-digital converter 15 to one of the buffer/registers 21A-21P for storage. Associated with each buffer/register 21A-21P is an associated compare/value register 21A′-21P′. The compare/value registers 21A′-21P′ store values that have been determined by the user. Each buffer/register 21A-21P is coupled through a mask 22A-22P to a first input terminal of comparators 23A-23P. Each compare/value register 21A′-21P′ is coupled through a mask 22A′-22P′ to a second input terminal of comparators 23A-23P. The output terminals of comparators 23A-23P are coupled to the central processing unit 28. The output signals of the comparators apply interrupt signals to the central processing unit 28. The values in the compare value registers can be hardwired, can be entered by the central processing unit, entered by the user, or some other storage method using available apparatus.

Referring next to FIG. 3, a second embodiment of the invention is illustrated. In this embodiment input signals are applied to multiplexer 12. A sequence/control unit 34 applies signals to the control terminals of a multiplexer 12. These control signals determine the multiplexer 12 input terminal that is coupled to the multiplexer 12 output terminal. The multiplexer 12 output terminal is applied to switch 16. The sequence/control unit 34 determines to which buffer/register unit 31A-31Q or to which buffer/register 32A″-32Q′ the output terminal of switch 16 is coupled. Each buffer/register 31A-31Q has an associated buffer/register 31A′-31Q′ associated therewith. Each buffer register 31A-31Q is coupled through a mask 32A-32Q to a first input terminal of a comparator 33A-33Q, while the associated buffer register 33A′-33Q′ is coupled through mask 32A′-32Q′ to a second terminal of comparator 33A-33Q. The output signals from comparators 33A-33Q are applied to the central processing unit 38. The output signals from the comparators 33A-33Q provide interrupt signals to the central processing unit and require a response.

In FIG. 2 and FIG. 3, the comparators are illustrated as comparing two input signals. As will be clear to those skilled in the art, each buffer/register can apply a plurality of signals (over a plurality of conducting leads) to the coupled comparator. The comparators compare related signals on a signal-by-signal basis. Each of the two groups of unmasked leads coupled to a comparator must provide coincident signals in order to generate an interrupt signal.

2. OPERATION OF THE PREFERRED EMBODIMENT

The present invention improves the processing capability in the following manner. In the present invention, an interrupt signal is provided only when the appropriate condition is detected. In the prior art, the central processing unit must at least periodically test the contents of the buffer/register to see if the condition(s) for generating an interrupt signal is present. Thus, testing will generate only a limited number of interrupt signals relative to the time an interrupt signal is generated, In the present invention, the interrupt signal is generated when the condition are appropriate and no signal is generated until the conditions are suitable. Thus, the impact on the central processing is limited to responding to an interrupt signal rather than determining if the conditions are appropriate for an interrupt signal.

In the embodiment illustrated in FIG. 2, a preselected signal is compared to a predetermined value. In the embodiment of the invention illustrated in FIG. 3, a preselected signal is compared to a second preselected signal. As will be clear, both embodiments can be combined in a single system, the burden of the implementation falling on the sequence/control unit.

While the invention has been described with respect to the embodiments set forth above, the invention is not necessarily limited to these embodiments. Accordingly, other embodiments, variations, and improvements not described herein are not necessarily excluded from the scope of the invention, the scope of the invention being defined by the following claims. 

1. Apparatus for comparing a digitized first signal with a second signal, the apparatus comprising: an analog-to-digital converter, the analog-to-digital converter digitizing a first signal; a first buffer/register coupled to the analog-to-digital converter, the first buffer/register storing the digitized first signal; a second buffer/register storing a digitized second value; and a comparator having first input terminal coupled to the first buffer/register, the comparator having a second input terminal coupled to the second buffer/register, the output terminal of the comparator providing comparison between the first and second signals.
 2. The apparatus as recited in claim 1 wherein the output signal of the comparator is an interrupt signal.
 3. The apparatus as recited in claim 1 further comprising; a control unit, and a multiplexer, the multiplexer coupling a plurality of input signals to an input terminal of the analog-to-digital converter, the control unit providing control signals to the multiplexer determining which input signal is coupled to the analog-to-digital converter input terminal.
 4. The apparatus as recited in claim 3 further comprising a switch coupled between the output terminal of the analog-to-digital converter and at least two of the first buffer/registers and the second buffer registers, the control unit applying signals to the switch determining to which buffer register unit the output terminal of the analog-to-digital converter is coupled.
 5. The apparatus as recited in claim 1 wherein the digitized second signal has preselected value.
 6. The apparatus as recited in claim 1 wherein the second buffer/register is coupled to an output terminal of the analog-to-digital converter, the second buffer/register storing digitized value of a second signal.
 7. The apparatus as recited in claim 1 further comprising: a first mask coupled between the first buffer register and the first input terminal of the comparator; and a second mask coupled between the second buffer/register and the second input terminal of the comparator.
 8. A method of providing a signal defining a relationship between a first signal and a second signal, the method comprising: digitizing a first signal; storing the digitized first signal in a first buffer/register; storing a digitized second signal in a second buffer/register; and comparing the first signal and the second signal by a comparator.
 9. The method as recited in claim 8 further comprising masking at least one of the first and the digitized signal.
 10. The method as recited in claim 8 comprising digitizing the first signal by an analog-to-digital converter.
 11. The method as recited in claim 8 wherein the second signal was digitized by the analog-to-digital converter.
 12. The method as recited in claim 8 further comprising generating an interrupt signal determined by the comparing of the first and the second signals.
 13. Apparatus for comparing a first signal and a first value, the apparatus comprising: an analog-to-digital converter, the analog-to-digital converter converting an analog input signal to a digitized output signal; a plurality of first buffer/registers; a switch unit coupled between an output terminal of the analog-to-digital converter and the plurality of buffer/registers; a control unit, the control unit determining to which buffer/register the output terminal of the analog-to-digital converter is coupled; a plurality of second buffer/registers, each second buffer/register associated with a second/buffer register; and a comparator coupled to each first buffer/register, second buffer pair, the comparator generating a preselected output signal when the contents of a buffer/register pair have a predefined relationship.
 14. The apparatus as recited in claim 13 wherein the output signal of a comparator is an interrupt signal.
 15. The apparatus as recited in claim 13, further comprising a multiplexer, the multiplexer coupling one of a plurality of input to an input terminal of the analog to digital converter in response to control signals from the control unit.
 16. The apparatus as recited in claim 13 further comprising mask units coupled between the buffer/register units and the comparator. 